Abstract
Measurement of microvascular perfusion with Intravoxel Incoherent Motion (IVIM) MRI is gaining interest. Yet, the physiological influences on the IVIM perfusion parameters (“pseudo-diffusion” coefficient D*, perfusion fraction f, and flow related parameter fD*) remain insufficiently characterized. In this article, we hypothesize that D* and fD*, which depend on blood speed, should vary during the cardiac cycle. We extended the IVIM model to include time dependence of D* = D*(t), and demonstrate in the healthy human brain that both parameters D* and fD* are significantly larger during systole than diastole, while the diffusion coefficient D and f do not vary significantly. The results non-invasively demonstrate the pulsatility of the brain’s microvasculature.
Highlights
The sensitivity of the Nuclear Magnetic Resonance (NMR) signal to nuclei motion has been well documented [1,2]
Magnetic Resonance Imaging (MRI) can exploit these principles to measure translational [5] and random motion, which can be measured with Intravoxel Incoherent Motion (IVIM) MRI [6], through the application of diffusion-weighted gradients followed by an EchoPlanar Imaging (EPI) signal readout [7]
The most common approach is to model the signal amplitude decay as function of the b-value as a biexponential decay [9]. This IVIM model permits the extraction of three microvascular perfusion parameters: the perfusion fraction f, which is related to blood volume; the pseudo-diffusion coefficient
Summary
The sensitivity of the Nuclear Magnetic Resonance (NMR) signal to nuclei motion has been well documented [1,2]. Magnetic Resonance Imaging (MRI) can exploit these principles to measure translational [5] and random motion, which can be measured with Intravoxel Incoherent Motion (IVIM) MRI [6], through the application of diffusion-weighted gradients followed by an EchoPlanar Imaging (EPI) signal readout [7]. The most common approach is to model the signal amplitude decay as function of the b-value as a biexponential decay [9]. This IVIM model permits the extraction of three microvascular perfusion parameters: the perfusion fraction f, which is related to blood volume; the pseudo-diffusion coefficient
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